This invention relates to a method for simultaneous removal of SO.sub.x and NO.sub.x from waste gas containing these oxides. More particularly, this invention relates to a method whereby sulfur oxide, SO.sub.x (SO.sub.2 and SO.sub.3), and nitrogen oxide, NO.sub.x (NO and NO.sub.2), which are air pollutants contained in minute amounts in the waste gas issuing from a boiler using a fossil fuel such as heavy oil or coal are simultaneously removed from said waste gas by use of an aqueous solution containing sulfuric acid, nitric acid and an iron compound as a catalyst.
For the removal of SO.sub.x from waste gas containing this oxide, various methods (such as those disclosed by U.S. Pat. No. 2,021,936 and 3,836,630, for example) have already been suggested and put to actual use. As regards the removal of NO.sub.x which is a substance causing photochemical smog and other types of environmental pollution, particularly in the treatment of large amounts of waste smoke from combustion of fossil fuels, there has not yet bee proposed any feasible method.
A primary object of the present invention, therefore, is to provide a commerically feasible method for enabling simultaneous removal of SO.sub.x and NO.sub.x present in the waste gas in a manner which is advantageous in terms of operation and economy.